A friction transmission belt is widely used for power transmission of auxiliary drive of an automobile, such as air compressor or alternator. In recent years, a requirement of silencing (quietness) against automobiles is increasing, and in particular, in a driving device, a sound other than an engine sound is regarded as a strange sound (or a noise), and therefore, a countermeasure to noise generation in the friction transmission belt is demanded. One of the strange sounds of the friction transmission belt is a slip noise generated when water intrudes into an engine room at running in rain or the like and the water attaches between a belt and a pulley, whereby the belt slips. A method for preventing such a slip noise in a wet (water-dampened) state is investigated.
For example, Japanese Patent No. 4763626 (Patent Document 1) discloses a friction transmission belt in which at least a friction transmission surface is constituted of a rubber composition in which a surfactant is blended in a prescribed proportion in an ethylene-α-olefin elastomer. In addition, JP-A-2011-252510 (Patent Document 2) discloses a friction transmission belt having a compressed rubber layer constituted of a rubber composition in which silica having a nitrogen adsorption specific surface area (BET) in the range of from 100 to 300 m2/g, either one of a polyamide short fiber and a para-aramid short fiber, and a cotton short fiber are blended in prescribed proportions in an ethylene-α-olefin elastomer. But, in these friction transmission belts, not only the slip noise in a wet state cannot be effectively suppressed yet, but the power transmission properties are not sufficient.